This invention relates to the control of the inlet air temperature for an internal combustion engine. In a conventional means for controlling such temperature, as illustrated in the King U.S. Pat. No. 3,444,847, a vacuum motor responsive to the low pressure of the engine inlet induction passage downstream of the throttle operates an inlet air proportioning valve to increase the ratio of preheated air to ambient air in the inlet flow to the engine when the inlet air temperature is less than a predetermined minimum.
An air bleed valve responsive to the inlet air temperature opens at a predetermined maximum temperature to bleed atmospheric air into the vacuum motor and thus into the induction passage to reduce the vacuum actuation of the motor and decrease the ratio to preheated to ambient inlet air. Such a system achieves an approximation of the desired inlet air temperature, but is sensitive to the pressure of the inlet induction passage and to the ambient temperature.
When a rise in the inlet air temperature calls for more ambient air, the air bleed opens to atmosphere, increases the operating pressure for the vacuum motor, and thereby causes the latter to open the proportioning valve to ambient air. Unless the air bleed valve has precise metering characteristics and opens gradually with increasing pressure, the proportioning valve will over react and admit too much ambient air. In any event, after the operating pressure for the vacuum motor and the temperature of the inlet air are stabilized by the position of the bleed valve, the induction vacuum operating the motor will change in consequence of changing engine operating conditions and call for more or less heated air as the case might be, even though the ambient air temperature remains constant.
The bleeding of atmospheric air into the inlet induction passage, as required by prior devices of the type described, may also impair drivability, especially for very small automobile engines where various vacuum operated devices already in use have preempted the vacuum capacity of the inlet induction passage. On the other hand, a convenient aspect of the above described prior devices arises from the fact that at wide open throttle operation when a maximum inlet flow of unheated air is desired, the pressure in the induction inlet passage is a maximum and automatically causes the proportioning valve to open fully to the ambient air and block the inlet of preheated air completely.
Important objects of the present invention are to provide an improved temperature sensor for controlling a vacuum motor to actuate a proportioning valve, whereby a more precise control of the inlet air temperature within a predetermined operating range is achieved then heretofore by comparable devices, wherein actuation of the vacuum motor is not directly susceptible to changes in the inlet induction passage pressure, and whereby the bleeding of atmospheric air into the inlet induction passage during operation of the vacuum motor is virtually eliminated except for negligible bleeding during transient situations.
Another object is to provide such a device that is responsive to operation at wide open throttle for actuating a proportioning valve to shut off the flow of preheated inlet air completely and to admit the maximum inlet flow of ambient air; or in the alternative, that is responsive to the ambient inlet air flow at wide open throttle to close the proportioning valve to preheated air and simultaneously to open the latter to admit the maximum of ambient air.
Another object is to provide such a device that is comparatively simple in structure and operation, economical to manufacture, and highly efficient in operation.